In standard wing junction connection areas or in particular areas such as near a passage of a frame, a pump opening, etc., the stiffeners must be stopped so that the structure assumes a flat plate geometry.
The stress supported by this stiffener is then transferred towards the underlying skin which is reinforced locally so as to withstand the excess load.
These “stiffener stops” cause local concentrations of stress likely to lead to tears or separations of the stiffener from the underlying skin. These specific areas must therefore be dimensioned with great prudence and consequently require reinforcements.
The problem to be solved is to define a stiffener stop shape that is compatible with the level of stress in the area and requires the least reinforcement.
The stops of conventional stiffeners are stops having a single slope.
In this type of stop, the problems involve balancing the behavior under traction with the behavior under compression. The lower the slope of the stop, the better is its behavior under traction but the poorer is its behavior under compression.
In another type of stiffener stop, which is also known, a double slope is provided, with the first slope being appreciably greater than the second.
While this solution yields the correct behavior toward compressive stress, the behavior under traction remains poor.
In fact, and as various studies have shown, the excess stress at the end of the stiffener remains directly related to the stress supported by the stiffener and, although the current stop designs make it possible to favor traction or compression, the variations in strength are relatively small and do not make it possible to obtain a really powerful stiffener stop, considering the type of panel that is involved, which is a self-stiffened carbon panel which is particularly inclined to separate.